[HIRSUTE][linux-riscv][PATCH v2] UBUNTU: SAUCE: RISC-V: prevent sbi_send_cpumask_ipi race with ftrace

[Andrea Righi]

On Wed, Aug 18, 2021 at 01:38:33PM +0100, Dimitri John Ledkov wrote:
> On Tue, Aug 17, 2021 at 7:41 AM Andrea Righi <andrea.righi at canonical.com> wrote:
> >
> > On Wed, Aug 11, 2021 at 10:23:27AM +0100, Dimitri John Ledkov wrote:
> > > From: Thadeu Lima de Souza Cascardo <cascardo at canonical.com>
> > >
> > > ftrace will patch instructions in sbi_send_cpumask_ipi, which is going to
> > > be used by flush_icache_range, leading to potential races and crashes like
> > > this:
> > >
> > > [    0.000000] ftrace: allocating 38893 entries in 152 pages
> > > [    0.000000] Oops - illegal instruction [#1]
> > > [    0.000000] Modules linked in:
> > > [    0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 5.11.0-1014-generic #14-Ubuntu
> > > [    0.000000] epc: ffffffe00000920e ra : ffffffe000009384 sp : ffffffe001803d30
> > > [    0.000000]  gp : ffffffe001a14240 tp : ffffffe00180f440 t0 : ffffffe07fe38000
> > > [    0.000000]  t1 : ffffffe0019cd338 t2 : 0000000000000000 s0 : ffffffe001803d70
> > > [    0.000000]  s1 : 0000000000000000 a0 : ffffffe0000095aa a1 : 0000000000000001
> > > [    0.000000]  a2 : 0000000000000002 a3 : 0000000000000000 a4 : 0000000000000000
> > > [    0.000000]  a5 : 0000000000000000 a6 : 0000000000000004 a7 : 0000000052464e43
> > > [    0.000000]  s2 : 0000000000000002 s3 : 0000000000000001 s4 : 0000000000000000
> > > [    0.000000]  s5 : 0000000000000000 s6 : 0000000000000000 s7 : 0000000000000000
> > > [    0.000000]  s8 : ffffffe001a170c0 s9 : 0000000000000001 s10: 0000000000000001
> > > [    0.000000]  s11: 00000000fffcc5d0 t3 : 0000000000000068 t4 : 000000000000000b
> > > [    0.000000]  t5 : ffffffe0019cd3e0 t6 : ffffffe001803cd8
> > > [    0.000000] status: 0000000200000100 badaddr: 000000000513f187 cause: 0000000000000002
> > > [    0.000000] ---[ end trace f67eb9af4d8d492b ]---
> > > [    0.000000] Kernel panic - not syncing: Attempted to kill the idle task!
> > > [    0.000000] ---[ end Kernel panic - not syncing: Attempted to kill the idle task! ]---
> > >
> > > Where ffffffe00000920e lies in the middle of sbi_send_cpumask_ipi.
> > >
> > > BugLink: https://bugs.launchpad.net/bugs/1934548
> > > Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo at canonical.com>
> > > Tested-by: Dimitri John Ledkov <dimitri.ledkov at canonical.com>
> > > Signed-off-by: Dimitri John Ledkov <dimitri.ledkov at canonical.com>
> > > ---
> > >
> > >  Patch can be applied to:
> > >  - Unstable
> > >  - Impish linux
> > >  - Impish linux-riscv
> > >  - Hirsute linux
> > >  - Hirsute linux-riscv
> > >  - Focal linux-riscv-5.11
> > >
> > >  Whichever are suitable for respins.
> > >
> > >  Changes since v1:
> > >  - Added BugLink, Tested-By, SOB
> >
> > Is there a particular reason to apply this to linux-riscv, instead of
> > just applying it to linux (linux-riscv would get it with the rebase)?
> >
> 
> This is actually not needed for v5.12+ kernels. See my follow-up
> patches that cherry pick fix from v5.12 that disables ftrace on all
> functions from sbi.o
> Hence this is not needed in any impish or unstable kernels.
> 
> It was applied against hirsute:linux-riscv only in the previous cycle,
> to respin it alone without respinning anything else for the upcoming

I see, thanks for the clarification Dimitri.

-Andrea